1. The Field of the Invention
The present invention relates generally to supported catalysts and methods for making and using such catalysts (e.g., in the direct synthesis of hydrogen peroxide). The support material is functionalized with an inorganic acid functional group to improve the bonding of the catalyst to the support.
2. The Related Technology
Hydrogen peroxide is a commercially important product which is widely used in the textile industry, paper industry, and chemical industry as a bleaching agent, biocide, and chemical reagent. Traditionally hydrogen peroxide has been manufactured through a process which includes multiple oxidation and reduction steps using alkylanthraquinones. This process is complicated and expensive because of the many steps involved, the large volumes of reagents, the relatively high cost of intermediates, and the production of inactive by-products.
Recently, efforts have been made to develop an alternative process whereby hydrogen peroxide is directly synthesized from hydrogen and oxygen using precious metal catalysts. The direct synthesis of hydrogen peroxide offers significant economic advantages because it avoids making intermediate products and does not need the use of reagents such as alkylanthraquinones.
One important aspect of a direct synthesis process is the catalyst, which must be able to selectively convert hydrogen and oxygen to hydrogen peroxide, with minimal production of water, a competing by-product that is thermodynamically favored over hydrogen peroxide. In general, catalysts for the direct synthesis reaction use palladium or a combination of palladium and platinum, as the active catalyst. These catalysts are generally used in the form of small particles dispersed on a solid catalyst support. Typically the support is a carbon-based material such as activated carbon.
Because of the high cost of the active catalyst metals, the metals need to be used efficiently and should be recoverable. Most existing direct synthesis processes use catalysts supported on a carbon-based powder and are used in a slurry-type reactor. The carbon powder catalyst is typically recovered from the liquid slurry using very efficient, but costly, filtration systems.
One disadvantage with slurry-type reactors is that they require continuous mixing. The continuous mixing increases attrition of the metal particles from the support. Metal particles that separate from the support are too fine to be recovered in the filtration process and are thus unrecoverable.
Another disadvantage of existing direct synthesis systems is the use of carbon as a support for the catalyst material. Carbon-based materials can degrade over time and/or combust in a high oxygen environment. The direct synthesis of hydrogen peroxide typically requires an oxygen feedstream. To avoid undesirable interaction between the oxygen feed stream and the carbon support, existing systems restrict the concentration of oxygen in the overall feed.
Therefore, what is needed is an improved supported catalyst that is efficient, better avoids attrition and leaching, and/or is more stable in a high oxygen environment.